Controlled combustion for regenerative reactors

ABSTRACT

The overall efficiency of a regenerative bed reverse flow reactor system is increased where the location of the exothermic reaction used for regeneration is suitably controlled. The present invention provides a method and apparatus for controlling the combustion to improve the thermal efficiency of bed regeneration in a cyclic reaction/regeneration processes. The process for thermal regeneration of a regenerative reactor bed entails
         (a) supplying the first reactant through a first channel means in a first regenerative bed and supplying at least a second reactant through a second channel means in the first regenerative bed,   (b) combining said first and second reactants by a gas mixing means situated at an exit of the first regenerative bed and reacting the combined gas to produce a heated reaction product,   (c) passing the heated reaction product through a second regenerative bed thereby transferring heat from the reaction product to the second regenerative bed.

FIELD OF THE INVENTION

The present invention relates broadly to regenerative reactors. Moreparticularly the invention relates to an improved process and apparatusfor controlling combustion for thermal regeneration of reverse flowregenerative reactors in a unique and thermally efficient way.

BACKGROUND OF THE INVENTION

Regenerative reactors are conventionally used to execute cyclic, hightemperature chemistry. Typically, regenerative reactor cycles are eithersymmetric (same chemistry or reaction in both directions) or asymmetric(chemistry or reaction changes with step in cycle). Symmetric cycles aretypically used for relatively mild exothermic chemistry, examples beingregenerative thermal oxidation (“RTO”) and autothermal reforming(“ATR”). Asymmetric cycles are typically used to execute endothermicchemistry, and the desired endothermic chemistry is paired with adifferent chemistry that is exothermic (typically combustion) to provideheat of reaction for the endothermic reaction. Examples of asymmetriccycles are Wulff cracking and Pressure Swing Reforming.

Conventional regenerative reactors deliver a stream of fuel, oxidant, ora supplemental amount of one of these reactants, directly to a locationsomewhere in the middle of the regenerative flow path of the reactor,without having that stream pass through regenerative beds or regions. Bymiddle of the regenerative flow path of the reactor, we mean a region ofthe reverse flow reactor that is in between two regenerative beds orregions, with the main regenerative flow passing from one of thesebodies to the other.

In most cases, this stream is introduced via nozzles, distributors, orburners that penetrate the reactor system using a means that isgenerally perpendicular to flow direction and usually through thereactor vessel side wall. For example, during the exothermic step in aconventional Wulff cracking furnace, air flows axially through theregenerative bodies, and fuel is introduced via nozzles that penetratethe side of the furnace, to combine with air (combusting and releasingheat) in an open zone between regenerative bodies. In a conventionalsymmetric RTO application, a burner is placed to provide supplementalcombustion heat in a location in between two regenerative bodies. Theburner combusts fuel from outside the reactor, either with the airpassing through the regenerative bodies, or using external air.

Attempts have been made to introduce a reactant of the exothermic stepto a location in the middle of the regenerative reactor via conduitsthat are positioned axially within one or more of the regenerativebodies. For example, Sederquist (U.S. Pat. No. 4,240,805) uses pipesthat are positioned axially within the regenerative bed to carry oxidant(air) to locations near the middle of the regenerative flow path.

All of these systems suffer disadvantages. Positioning nozzles,distributors, or burners in the middle of the regenerative flow path ofthe reactor diminishes the durability of the reactor system. Nozzles,distributors, and burners all rely on carefully-dimensioned passages toregulate flow in a uniform manner, or to create the turbulence or mixingrequired to evenly distribute the heat that results from the exothermicreaction they support. By function in a regenerative reactor, thesenozzles, distributors, are located at the highest-temperature part ofthe reactor. It is very difficult to fabricate and maintaincarefully-dimensioned shapes for use at high temperatures. If thenozzles or distributor loses its carefully-dimensioned shape, it will nolonger produce uniform flame temperatures.

A further disadvantage of using nozzles, distributors, or burners tointroduce one or more reactant directly into the middle of theregenerative flow path of the reactor is that such an arrangementbypasses that reactant around the regenerative flow path, and thuseliminates the possibility of using the regenerative reactor system topreheat that reactant stream. The fundamental purpose of a regenerativereactor system is to execute reactions at high efficiency byrecuperating product heat directly into feeds. Bypassing some fractionof the feed to the reactor around the regenerative system thus reducesthe efficiency potential of the reactor system.

It is an object of the present invention to provide a means foroperating a regenerative reactor system that alleviates these problemsof the conventional design and operation of a regenerative reactorsystem.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for controllingthe location of the exothermic reaction used for regeneration inreverse-flow, cyclic reaction/regeneration processes such as pressureswing reforming. The process for thermal regeneration of a regenerativereactor bed entails:

-   -   (a) supplying the first reactant through a first channel means        in a first regenerative bed and supplying at least a second        reactant through a second channel means in the first        regenerative bed,    -   (b) combining said first and second reactants by a gas mixing        means situated at an exit of the first regenerative bed and        reacting the combined gas to produce a heated reaction product,    -   (c) passing the heated reaction product through a second        regenerative bed thereby transferring heat from the reaction        product to the second regenerative bed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of thermal regeneration in areverse flow reactor.

FIG. 2 is a diagrammatic illustration of a regenerative bed reactor withmeans for controlling the location of the exothermic reaction.

FIG. 3 illustrates an axial view of a gas distributor.

FIG. 4 is an axial view of gas mixer. FIG. 4 a is a cutoutcross-sectional view of a portion of FIG. 4.

FIG. 5 a is a diagrammatic illustration of a conventional RegenerativeThermal Oxidation Reactor; 5 b is an illustration of a RTO Reactor withcontrolled combustion.

FIG. 6 a is a graph of temperature versus distance from the top of theregenerative bed for an embodiment of the present invention; FIG. 6 b isa graph of temperature versus distance from the top of the regenerativebed for a fuel insertion device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The basic two-step asymmetric cycle of a reverse flow regenerative bedreactor is depicted in FIGS. 1 a and 1 b in terms of a single bed orreactor having two zones, a first zone, or reaction zone (1) and asecond zone, or recuperator zone (7). Both the reaction zone (1) and therecuperator zone (7) contain regenerative beds. Regenerative beds, asused herein, are intended to comprise material that are effective instoring and transferring heat. The term regenerative reactor bed(s)means a regenerative bed that may also be used for carrying out achemical reaction. Regenerative beds are generally known in the art andmay comprise packing material such as glass or ceramic beads or spheres,metal beads or spheres, ceramic or metal honeycomb materials, ceramictubes, monoliths, and the like.

As shown in FIG. 1 a, at the beginning of the first or “reaction” stepof the cycle, the reaction zone (1) is at an elevated temperature andthe recuperator zone (7) is at a lower temperature than the reactionzone (1). A reactant feed is introduced via a conduit (15), into a firstend (3) of the reaction zone (1).

This feed stream picks up heat from the bed and is reacted, optionallyover catalyst, to produce the desired reaction, such as steam reforming,for example. As this step proceeds, a temperature profile (2) is createdbased on the heat transfer properties of the system. When the bed isdesigned with adequate heat transfer capability, this profile has arelatively sharp temperature gradient, which gradient will move acrossthe reaction zone (1) as the step proceeds.

Reaction gas exits the reaction zone (1) through a second end (5) at anelevated temperature and passes through the recuperator zone (7),entering through a first end (11) and exiting at a second end (9). Therecuperator zone (7) is initially at a lower temperature than thereaction zone (1). As the reaction gas passes through the recuperatorzone (7), the gas is cooled to a temperature approaching the temperatureof the zone substantially at the second end (9), which is approximatelythe same temperature as the regeneration feed introduced during thesecond step of the cycle here illustrated as via conduit (19). As thereaction gas is cooled in the recuperator zone (7), a temperaturegradient (4) is created in the zone's regenerative bed(s) and movesacross the recuperator zone (7) during this step. The reaction gas exitsthe recuperator zone at (17). The second step of the cycle, referred toas the regeneration step then begins.

The regeneration step is illustrated in FIG. 1 b. Regeneration entailstransferring heat from the recuperator zone to the reaction zone tothermally regenerate the reaction beds for the subsequent reactioncycle. Regeneration gas enters recuperator zone (7) here illustrated asvia conduit (19), and flows through the recuperator zone and into thereaction zone. In doing so, the temperature gradients (6) and (8) moveacross the beds similar but in opposite directions to the temperaturegradients developed during the reaction cycle. Fuel and oxidant combustat a region proximate to the interface (13) of the recuperator zone (7)and the reaction zone (1). The heat recovered from the recuperator zonetogether with the heat of combustion is transferred to the reactionzone, thermally regenerating the regenerative reaction beds disposedtherein.

In a conventional reverse flow regenerative reactor, fuel and oxidantare typically combined at the combustion zone by injecting either fuel,or oxidant, or both, into the combustion zone, typically via nozzles orinjectors through the vessel side walls.

FIG. 2 illustrates means for controlling the combustion of fuel andoxidant to achieve efficient regeneration of the reactor system heat.FIG. 2 depicts a single reactor system, operating in the regenerationcycle.

Referring to the Figure, recuperator zone (27) has gas channel means(28) for channeling two or more gases upon entry to a first end (29) ofthe recuperator zone (27) through the regenerative bed(s) disposedtherein. A first gas (30) enters a first end of a plurality of channelmeans (28). The gas channel means (28) may comprise channels or tubes orother means suitable for maintaining gases substantially separated fromat least a second gas (described hereinafter) while axially transitingthe regenerative bed(s) of recuperator zone (27). A gas distributor (31)directs a second gas stream (32) to select channels, here illustrated aschannels (33). The result is that at least a portion of gas stream (33)is kept separate from gas stream (30) during its axial transit of therecuperator zone (27). In a preferred embodiment, the regenerativebed(s) of the recuperator zone comprise the channel means. Thereby, theat least two gases that transit the channel means are transiting theregenerative bed(s).

As used in the present invention, gases (30) and (32) comprise tworeactants that result in an exothermic reaction when combined, forexample a fuel gas and an oxidant gas that result in combustion whencombined. By keeping these reactants substantially separated, thepresent invention controls the location of the heat release that occursdue to exothermic reaction. By “substantially separated”, we mean thatat least 50%, and preferably at least 75% of the reactant in the firstgas (30) has not become consumed by reaction with the second gas (32),and that at least 50%, and preferably at least 75% of the reactant inthe second gas (32) has not become consumed by reaction with the firstgas (30), by the point at which these gases have completed their axialtransit of the recuperator zone (27). In this manner, the majority ofthe first gas (30) is kept isolated from the majority of the second gas(32), and the majority of the heat release from the reaction ofcombining gases (30) and (32) will not take place until the gases haveexited from the recuperator zone (27). In a preferred embodiment, thechannel means structure of recuperator zone (27) comprise a plurality ofindividual channels oriented substantially parallel to the direction offlow. Such channel structures are provided, for example, by regenerativebeds comprised of extruded honeycomb monoliths, or comprised of stackedlayers of corrugated materials, as is known in the art. Such channelstructures provide a high level of separation of gases in one channelfrom the next. Alternatively, the regenerative beds of the recuperatorzone may comprise packing material or a porous ceramic monolith that isstructured to provide substantial separation of the gases (30) and (32).

In a preferred embodiment, the channel means (28) and (33) comprisematerials that provide adequate heat transfer capacity to create thetemperature profiles (4) and (8) illustrated in FIG. 1 at the spacevelocity conditions of operation. Adequate heat transfer rate ischaracterized by a heat transfer parameter ΔT_(HT), below about 500° C.,more preferably below about 100° C. and most preferably below about 50°C. The parameter ΔT_(HT), as used herein, is the ratio of thebed-average volumetric heat transfer rate that is needed forrecuperation, to the volumetric heat transfer coefficient of the bed,h_(v). The volumetric heat transfer rate (e.g. cal/cm³ sec) that issufficient for recuperation is calculated as the product of the gas flowrate (e.g. gm/sec) with the gas heat capacity (e.g. ca./gm ° C.) anddesired end-to-end temperature change (excluding any reaction, e.g. °C.), and then this quantity divided by the volume (e.g. cm³) of therecuperator zone (27) traversed by the gas. The ΔT_(HT) in channel means(28) is computed using gas (30), channel means (33) with gas (32), andtotal recuperator zone (27) with total gas. The volumetric heat transfercoefficient of the bed, h_(v), is known in the art, and is typicallycalculated as the product of a area-based coefficient (e.g. cal/cm²s°C.) and a specific surface area for heat transfer (a_(v), e.g. cm²/cm³),often referred to as the wetted area of the packing.

In a preferred embodiment, channel means (28) and (33) comprise ceramicchannels or tubes, capable of withstanding temperatures exceeding 600°C., more preferably 1000° C., and most preferably 1300° C. Mostpreferably, channel means (28) comprise a ceramic honeycomb, havingchannels running the axial length of the recuperator zone (27).

The recuperator zone (27) may include packed bed or foam monolithmaterials (not shown) that allow dispersion of reactants perpendicularto flow direction, so long as radial dispersion is low enough to keepreactants substantially separated during pass through the recuperator.Calculation of radial dispersion and mixing in bed media is known in theart.

Referring momentarily to FIG. 3, there is shown an axial view of a gasdistributor (31) having apertures (36). Referring to both FIGS. 2 and 3,apertures (36) direct the second gas (32) preferentially to selectchannels (33). In a preferred embodiment, apertures (36) are alignedwith, but are not sealed to, the openings of select channels (33).Nozzles or injectors (not shown) may be added to the apertures (36) thatare suitably designed to direct the flow of the second gas (32)preferentially to the select channels (33). By not “sealing” the gasdistributor apertures (36) (or nozzles/injectors) to the select channels(33), these channels may be utilized during the reverse flow or reactioncycle, increasing the overall efficiency of the system. This “open” gasdistributor (31) is also preferred over a “closed” system to facilitateadaptation to multiple reactor systems, where the reactor/recuperatorbeds may rotate in and out of a gas stream for processing.

The first gas (30) and second gas (32) transit the recuperator zone (27)via channels (28) and (33). Heat, stored in the recuperator zone fromthe previous cycle, is transferred to both the first and second gas(es).The heated gases are then introduced into gas mixing means (44).

Gas mixing means (44), located between the recuperator zone (27) and thereaction zone (21), functions to mix gas stream (30) and (32), at ornear the interface of the reaction zone (21) and the gas mixer means(44).

The mixer means (44) is constructed or fabricated of a material able towithstand the high temperatures expected to be experienced in thereaction zone. In a preferred embodiment, mixer means (44) isconstructed from a material able to withstand temperatures exceeding600° C., more preferably 1000° C., and most preferably 1300° C. Forsteam reforming of methane, for example, reaction zone temperaturestypically exceed 1000° C. In a preferred embodiment, mixer means (34) isconstructed of ceramic material(s) such as alumina or silicon carbidefor example.

Referring to FIG. 4, there is shown an axial view of one configurationof the gas mixing means (44) together with a cut-away view 4 a of one ofswirl-mixer means (47).

The gas mixer means (44) shown here comprises sections (45) having swirlmixer means (47) located within the sections (45). In a preferredembodiment, sections (45) are substantially equal in cross sectionalarea, and swirl mixer means (47) are centrally located within thesections (45).

Gas mixer sections (45) are positioned to segment the gas flow of aplurality of gas channel means (28) and (33). In a preferred embodiment,sections (45) have substantially equal cross sectioned area tofacilitate intercepting gas flow from a substantially equal number ofgas channel means (28) and (33). Also in a preferred embodiment, gaschannel means (28) and (33) are distributed within recuperator (27) suchthat each of the sections (45) intercepts gas flow from a substantiallyequal fraction of both first gas channel means (28) and second gaschannel means (33). Expressed mathematically, one can define f_(Ai) asthe fraction of total cross sectional area encompassed by section i,f_(28i) as the fraction of total channel means (28) intercepted bysection i, and f_(33i) as the fraction of total channel means (33)intercepted by section i. In a preferred embodiment, for each section i,the values f_(28i), and f_(33i) will be within about 20% of (i.e.between about 0.8 and 1.2 times the value of) f_(Ai), and morepreferably within about 10%. One can further define f_(30i) as thefraction of gas stream (30) intercepted by section i, and f_(32i) as thefraction of gas stream (32) intercepted by the section i. In a morepreferred embodiment, for each section i, the values of f_(30i), andf_(32i) will be within about 20% of f_(Ai), and more preferably withinabout 10%.

Referring momentarily to FIG. 4 a, there is shown a cut out section ofan individual gas mixer section (45) with swirl mixer means (47). Whilethe present invention may utilize a gas mixer means known to the skilledartisan to combine gases from the plurality of gas channel means (28)and (33), a preferred embodiment of this invention minimizes open volumeof the gas mixer means (44) while maintaining sufficient mixing anddistribution of the mixed gases. The term open volume means the totalvolume of the swirl mixers (47) and gas mixer section (45), less thevolume of the material structure of the gas mixer. Accordingly, gasmixer section (45) and swirl mixer means (47) are configured to minimizeopen volume while concurrently functioning to provide substantial gasmixing of the gases exiting gas channel means (28) and (33). In apreferred practice of the invention, gas mixer segment (45) dimensions Land D, are tailored to achieve sufficient mixing and distribution ofgases (31) and (32) while minimizing open volume. Dimension ratio L/D ispreferably in the range of 0.1 to 5.0, and more preferably in the rangeof 0.3 to 2.5. For general segments of area A, a characteristic diameterD can be computed as 2(A/π)^(1/2).

In addition, the total volume attributable to the gas mixer (44) ispreferably tailored relative to the total volume of the recuperator bedand reforming bed. Gas mixer (44) preferably has a total volume lessthan about 20%, and more preferably less than 10% of the combined volumeof the recuperator zone (27), reaction zone (21) and the gas mixer means(44).

Referring again to FIG. 2, the gas mixer means (44) so configuredcombines gases from channels (33) and (28), and redistributes thecombined gas across and into reaction zone (21).

In a preferred embodiment, first and second gases comprise fuel andoxidant. Fuel may comprise hydrogen, carbon monoxide, hydrocarbons,oxygenates, petrochemical streams, or mixtures thereof. Oxidanttypically comprises a gas containing oxygen, commonly mixed with N₂ asin air. Upon mixing the fuel and oxidant at gas mixer (44), the gasescombust, with a substantial proportion of the combustion occurringproximate to the entrance to the reaction zone (21).

The combustion of the fuel and oxygen-containing gas proximate to theentrance of the reaction zone creates a hot fluegas that heats (orre-heats) the reaction zone (21) as the flue gas travels across thatzone. The composition of the oxygen-containing gas/fuel mixture isadjusted to provide the desired temperature of the reaction zone. Thecomposition and hence temperature is adjusted by means of the proportionof combustible to non-combustible portions of the mixture. For example,non-combustible gases such as H₂O, CO₂, and N₂ can be added to themixture to reduce combustion temperature. In a preferred embodiment,non-combustible gases comprise steam, flue gas, or oxygen-depleted airas at least one component of the mixture. The hot combustion productpasses through reaction zone. The flow of combustion product establishesa temperature gradient within the reaction zone, which gradient movesaxially through the reaction zone. At the beginning of the regenerationstep, this outlet temperature will be substantially equal (typicallywithin 25° C.) to the inlet temperature of the reforming feed of thepreceding, reforming, step. As the regeneration step proceeds, thisoutlet temperature will increase slowly and then rapidly as thetemperature gradient reaches the end of the reforming bed, and can be50-500° C. above the temperature of the reaction feed by the end of thestep.

The controlled combustion reverse flow regenerative reactor systemdescribed herein is particularly well suited for steam reformingreactions such as Pressure Swing Reforming as described in U.S. patentapplication 2003/0235529A1.

FIG. 1 may be used to illustrate its application to Pressure SwingReforming. At the beginning of the first step of the cycle, also calledthe reforming step, the reforming zone (1) is at an elevated temperatureand the recuperating zone (7) is at a lower temperature than thereforming zone (1). A hydrocarbon-containing feed may be introduced viaa conduit (15), into a first end (3) of the reforming zone (1) alongwith steam. The hydrocarbon may be any material that undergoes theendothermic steam reforming reaction including methane, petroleum gases,petroleum distillates, kerosene, jet fuel, fuel oil, heating oil, dieselfuel and gas oil, gasoline and alcohols. Preferably, the hydrocarbonwill be a gaseous material comprising methane and/or hydrocarbons thatare in a gaseous state at the temperature and pressure of the reactor.Preferably, the steam will be present in proportion to the hydrocarbonin an amount that results in a steam to carbon ratio between about 1 andabout 3 (considering only carbon in the hydrocarbon, not carbon in CO orCO₂ species that may be present).

This feed stream picks up heat from the bed and is converted over thecatalyst and heat to synthesis gas. As this step proceeds, a temperatureprofile (2) is created based on the heat transfer properties of thesystem. When the bed is designed with adequate heat transfer capability,as described herein, this profile has a relatively sharp temperaturegradient, which gradient will move across the reforming zone (1) as thestep proceeds.

Synthesis gas exits the reforming bed (1) through a second end (5) at anelevated temperature, passes through mixer (44), as shown in FIG. 2, andthen passes through the recuperating zone (7), entering through a firstend (11) and exiting at a second end (9). The recuperating zone (7) isinitially at a lower temperature than the reforming zone (1). As thesynthesis gas passes through the recuperating zone (7), the synthesisgas is cooled to a temperature approaching the temperature of the zonesubstantially at the second end (9), which is approximately the sametemperature as the regeneration feed introduced during the second stepof the cycle via conduit (19) (e.g., from about 20° C. to about 600°C.). As the synthesis gas is cooled in the recuperating zone (7), atemperature gradient (4) is created and moves across the recuperatingzone (7) during this step.

At the point between steps, the temperature gradients have movedsubstantially across the reforming zone (1) and the recuperating zone(7). The zones are sized so that the gradients move across both incomparable time during the above reforming step. The recuperating zone(7) is now at the high temperature and the reforming zone (1) is at lowtemperature, except for the temperature gradient that exists near theexits of the respective zones. The temperature of the reforming zone (1)near the inlet end (3) has now been cooled to a temperature thatapproaches the temperature of the hydrocarbon feed that has beenentering via conduit (15) (e.g., from about 20° C. to about 600° C.).

After the synthesis gas is collected via an exit conduit (17) at thesecond end (9) of the recuperating zone (7), the second step of thecycle, also called the regeneration step begins. The regeneration step,illustrated in FIG. 1 b, basically involves transferring the heat fromthe recuperator bed (7) to the reformer bed (1) and an exothermicreaction at the interface (13). In so doing, the temperature gradients 6and 8 move across the beds similar to but in opposite directions togradients 2 and 4 during reforming. A regeneration gas comprising anoxygen-containing gas and fuel are introduced into the second end (9) ofthe recuperating zone (7). As described in reference to FIG. 2, theoxygen containing gas is channeled through the recuperator zonesubstantially separated from the fuel. The fuel and oxidant are combinedby means of mixer (44) at interface (13), combusting substantially atthe interface of the recuperator zone (7) and the reaction zone (1).Combustion occurs at a region proximate to the interface (13) of therecuperation zone (7) and the reforming zone (1). The term, “regionproximate”, in the present invention, means the region of the PSR bedsin which regeneration step combustion will achieve the following twoobjectives: (a) the heating of the reforming zone such that end (5) ofthe reforming zone is at a temperature of at least 800° C., andpreferably at least 1000° C. at the end of the regeneration step; and(b) the cooling of the recuperation zone to a sufficient degree that itcan perform its function of accepting synthesis gas sensible heat in thesubsequent reforming step. Depending on specific regenerationembodiments described herein, the region proximate to the interface caninclude from 0% to about 50% of the volume of the recuperation zone (7),and can include from 0% to about 50% of the volume of the reforming zone(1). In a preferred embodiment of the present invention, greater than90% of the regeneration step combustion occurs in a region proximate tothe interface, the volume of which region includes less than about 20%the volume of the recuperating zone (7) and less than about 20% thevolume of reforming zone (1).

The reforming zone is now, once again, at reforming temperaturessuitable for catalytic reforming.

EXAMPLE 1

The following is an example of an asymmetric reverse-flow reactor systemused to perform methane steam reforming. The reactor is used in theorientation shown in FIG. 2, with the endothermic reforming step flowingupwards through the reactor (not shown) and exothermic fuel combustionstep flowing downwards through the reactor (as illustrated). Thediameter of the reactor (inside of insulation) is 2.5 inches. The bedcomponents have diameters of about 2.5 inches to fit within theinsulation. The reforming or reaction zone (21) is comprised of a 2.5inch length of 400 cells/in² honeycomb that has been wash-coated withreforming catalyst.

The recuperator zone (27) was constructed of several lengths ofuncatalyzed 400 cells/in² honeycomb located at the inlet end that arestacked for a combined height of 1.19 inches.

A distributor means (31) illustrated in FIGS. 2 and 3 was located abovethe recuperator honeycomb. It comprised a 1.8 inch diameter ring of 0.25inch (OD) stainless steel tubing with one spoke of tubing extending tothe center, and seven metering orifices sized at 0.034 inch IDmanufactured on the lower side of the ring; one in the middle on thespoke and six spaced equally around the ring. During the regenerationcycle, the orifices in the ring release the fuel (32) in seven streamslocated approximately over the centers of each of the channel means (33)(and thereby) the seven mixer segments. Combustion air (30) flowed downaround distributor (31) from above into channel means (28).

After transiting the recuperator zone, gases (30) and (32) were combinedby gas mixer (44). The mixer (44) was constructed as illustrated in FIG.4, with seven segments; one central and six around the perimeter. Lengthof divider (49) was set at about 0.73 inches, to provide for equalcross-sectional area in the seven segments. Segment height (L) was 0.375inches, while segment characteristic (D) was 0.95 inches, resulting in asegment L/D of about 0.40. A 0.500 inch length region of 0.125 inchinert alumina beads is interposed between the gas mixer and the upperend of the reaction zone to further disperse the mixed gases.

Because the mixer (44) was designed to have equal segment areas, theF_(Ai) value for each of the seven segments was 1/7 or 14.3%. Since eachdistributor orifice principally feeds one segment, the values forF_(33i) were defined by the performance of the distributor. Prior tooperation, the performance of the distributor (31) was measured outsideof the reactor. The F_(33i) values for the distributor were: 15.5% forthe center orifice, and 13.9%, 14.5%, 14.1%, 14.1%, 13.8%, 14.3% for thesix orifices around the ring. This represents a maximum deviation fromF_(Ai) of 8.3%.

Valves above and below the reactor were used to control the alternatingflows of the reverse-flow operation. The reverse-flow reactor system wasrun with the following cycle: 15 seconds of regeneration consisting of aflow of oxidant (30) comprising 46.8 SLM air and 137. SLM nitrogen and aflow of fuel (32) comprising 16 SLM of hydrogen; followed by 13.5seconds of reforming (upflow) comprising 11.9 SLM of methane and 28.2SLM of steam; followed by 1.5 seconds of product purge (upflow)comprising 28.2 SLM of steam. The regeneration cycle was operated atabout 1.7 atm abs, and the reform cycle at 2.0 atm abs. All streams arefed to the reactor at a temperature of about 250° C.

The reverse flow reactor was operated in this configuration with flowsdescribed above, and temperatures were measured at five consecutivetimes during the regeneration step, at three locations within therecuperator zone (27) and one location proximate to the interface (13)between recuperation and reforming zones, all as measured from the topof the first regenerative honeycomb monolith bed within recuperator zone(27). Temperature measurements are shown in FIG. 6 a.

A comparative example was performed using a fuel insertion tube coupledto a fuel distributor disk, located in between the reforming andrecuperating zones, in lieu of the gas distributor, channel means andgas mixer. For this example, the bottom 0.19 inches of the recuperatorzone (27) was replaced with a 0.5 inch long regenerative bed containing0.125 inch diameter alumina spheres. So configured, the comparativeexample fuel insertion tube and distributor injected fuel gas to theregion between the recuperator zone (27) and the reformer zone (21). Theapparatus of the comparative example was operated substantiallyidentical to the above Example, with substantially similar temperaturemeasurements shown in FIG. 6 b.

The controlled combustion system described herein may be employed forother, asymmetric reverse flow regenerative reactor systems. Theregeneration (exothermic) step, described with respect to FIG. 1B andFIG. 2, can be combustion, as described above for pressure swingreforming, or can other exothermic reactions such as partial oxidation.As applied to partial oxidation, the streams that are fed during theexothermic step comprise a hydrocarbon-containing stream, and a streamwith sub-stoichiometric amount of oxidant. By sub-stoichiometric, wemean less oxidant than would be needed to fully oxidize thehydrocarbon-containing stream. These two streams would be maintainedsubstantially separated as described in respect of FIG. 2 above.Typically the stream that has the lesser flow rate will be fed as stream(32), and the greater as stream (30). The endothermic reaction step canbe steam reforming, as described above for pressure swing reforming, orcan be other endothermic reactions. During the endothermic reactionstep, as described with respect to FIG. 1A, the endothermic reactant isfed via conduit 15, is heated and reacted in reaction zone (1), iscooled in recuperation zone (7), with reaction products being collectedvia conduit (17). Catalyst may be used in one or both zones tofacilitate reaction. Preferred endothermic reactions for use with thepresent invention include steam reforming, dry (CO2) reforming,pyrolysis, catalytic cracking, dehydrogenation, and dehydration.Preferred pyrolysis reactions for use with the present invention includesteam cracking reactions such as ethane, naphtha, or gas oil cracking,hydropyrolysis reactions such as methane hydropyrolysis to acetylene,and non-hydrocarbon cracking reactions such as H2S pyrolysis to hydrogenand sulfur. Preferred dehydrogenation reactions for use with the presentinvention include alkane dehydrogenations such as propanedehydrogenation and alkyl-aromatic dehydrogenations such as ethylbenzene dehydrogenation. Preferred dehydration reactions for use withthe present invention include methanol and ethanol dehydration.

EXAMPLE 2

The controlled combustion reverse flow regenerative reaction may beemployed for Regenerative Thermal Oxidation (“RTO”) processes. The RTOprocesses are conventionally used to combust relatively low levels ofcontaminants from a larger stream of air. FIG. 5 a illustrates theconventional configuration of an RTO reactor, FIG. 5 b a RTO reverseflow reactor with controlled combustion.

Referring to FIG. 5 a, the process is generally comprised of tworegenerative bodies (501, 502) with a burner (503) in between.Contaminated air (504) is heated in the first regenerative body (501),supplemental heat is provided by the combustion of fuel (505) in burner(503) situated between the two regenerative bodies, and the products arecooled to exit the second regenerative body as clean air (506). Frequentflow reversal, switching to streams (504 a & 506 a), is used to keep thesensible heat (of heating or cooling) moving back and forth between thetwo bodies (501, 502). All or part of the regenerative bed system (501,502) may include catalyst in to improve the incineration of thecontaminants. Typically, the RTO system includes distribution volume(507) at the cold entry of each regenerative body, and an open volume(508) in which the burner-driven combustion occurs.

Referring now to FIG. 5 b in the present invention, the two regenerativebodies (501, 502) are constructed with packing having substantiallyparallel channels, and those channels are oriented substantiallyco-axial with the direction of flow. In between the two regenerativebodies is located the mixing device (509). Contaminated air (504) isheated in the first regenerative bed. Fuel distribution means (510),located in the distribution volume (507) at the cold entry of eachregenerative bed, places supplemental fuel (505) into a select number ofchannels within the regenerative body. This fuel is heated in the firstregenerative body and is then mixed with the heated contaminated air inthe mixer (509) resulting in combustion and release of heat into thestream. Combustion products are cooled to exit the second regenerativebed as clean air (506). Frequent flow reversal, switching to streams(504 a, 510 a, 507 a, 505 a, 506 a), is used to keep the sensible heat(of heating or cooling) moving back and forth between the two bodies.All or part of the regenerative bed system (501, 502) may includecatalyst to improve the incineration of the contaminants.

As illustrated, there does not need to be a seal between the distributor(510) and the regenerative body (501). Combustion will not occur untilgases have been heated which heating occurs during its transit of therecuperator zone. As long as the majority of the fuel is isolated fromthe majority of the air as taught herein, then the majority of the heatrelease will not take place until the mixer (509). As long as themajority of the heat release occurs at or after mixer (509), theregenerative reactor will function at high efficiencies.

EXAMPLE 3 Autothermal Reforming (“ATR”)

The controlled combustion reverse flow regenerative reactor may beemployed for Autothermal Reforming (“ATR”). In the RTO application, theamount of oxidant (air) is conventionally many times greater than theamount needed for stoichiometric combustion of the contaminants and thesupplemental fuel. Also, the incoming contaminated air is near ambientconditions of pressure and temperature. For ATR, the oxidant is presentin sub-stoichiometric amounts, and may be absent of any diluents. Thefuel is not a supplementary material, but a feedstock to be reformed.Pressures and feed temperature are typically substantially higher. Thesedifferences notwithstanding, the application includes substantially thesame components as the RTO application and is illustrated in FIG. 5 b.Preferably, the feed stream (504) in largest volume flow rate will bedistributed into the majority of regenerative body (501) channels viathe entry distribution volume (507). The feed stream (505) having lowervolume flow rate is distributed via distributor (510) into selectchannels. The oxidant, fuel and optionally steam or CO2 are heated inregenerative body (501) and are mixed at the mixer (509) whereupon theexothermic autothermal reforming reactions occur. Reactions can beassisted by catalyst placed in all or part of the regenerative bodies(501 and 502). Reaction is substantially confined within theregenerative body (502) following the mixer, and cooling occurs withinthe regenerative body (502) following the mixer. Cool syngas is theproduct (506) of the reactor. Frequent flow reversal (via streams 504 a,505 a, 506 a) is used to keep the sensible heat (of heating or cooling)moving back and forth between the two bodies.

Although the invention has been described in detail herein, the skilledpractitioner will recognize other embodiments of the invention that arewithin the scope of the claims.

1. A process for controlling the location of an exothermic reactionbetween two or more reactants in a cyclic reverse-flow reactor systemcomprising: (a) supplying the first reactant through a first channelmeans in a first regenerative bed and supplying at least a secondreactant through a second channel means in the first regenerative bed,(b) combining said first and second reactants by a gas mixing meanssituated at an exit of the first regenerative bed and reacting thecombined gas to produce a heated reaction product, (c) passing theheated reaction product through a second regenerative bed therebytransferring heat from the reaction product to the second regenerativebed.
 2. The process of claim 1 wherein said cyclic reverse flow reactorsystem comprises a reaction zone and a recuperation zone, and a gasmixer means situated therebetween.
 3. The process of claim 1 whereinsaid first and second channel means axially traverse the firstregenerative bed and pass the first and second gas to the gas mixermeans.
 4. The process of claim 3 wherein the gas mixer means comprisessegments, axially aligned with the first and second channel means. 5.The process of claim 4 wherein the gas mixer segment have axial crosssectioned areas that are about equal in area.
 6. The process of claim 5wherein the gas mixer segments include gas swirl means that function tomix gases flowing therethrough.
 7. The process of claim 6 wherein gasfrom the first and second channel means flow into the gas mixersegments, combining therein, combusting and passing through the secondregenerative beds.
 8. The process of claim 7 wherein the gas from firstand second channel means are each divided about equally among the gasmiser segments.
 9. The process of claims 2 or 7 wherein said combustingoccurs proximate to an interface between the gas mixer means and thesecond regenerative bed.
 10. The process of claims 2 or 4 wherein thegas mixer means is constructed from material able to withstandtemperatures in excess of about 600° C.
 11. The process of claim 10wherein the gas mixer means is constructed from material able towithstand temperatures in excess of about 1000° C.
 12. The process ofclaim 11 wherein the gas mixer is constructed from material able towithstand temperatures in excess of about 1300° C.
 13. The process ofclaim 9 wherein the gas mixer comprises a ceramic.
 14. The process ofclaim 2 wherein the reaction zone has a volume A, and recuperator zonehas a volume B, and the gas mixer means has a volume C, whereby volume Cis less than about twenty percent of volume A plus volume B plus volumeC.
 15. The process of claim 14 wherein volume C is less than about tenpercent of volume A plus volume B plus volume C.
 16. The process ofclaim 4 wherein the gas mixer segments have an axial cross sectionalarea whose linear dimension is D, and an axial length L, the ratio of Lto D ranges from about 0.1 to about 5.0.
 17. The process of claim 4wherein the gas mixer segments have an axial cross sectional area whoselinear dimension is D, and an axial length L, the ratio of L to D rangesfrom about 0.3 to about 2.5.
 18. The process of claim 1 wherein saidfirst and second channel means function to maintain said first andsecond reactants separated such that at least fifty percent of suchgases have not reacted in the first regenerative bed while transitingthe first regenerative bed.
 19. The process of claim 17 wherein at leastseventy-five percent of the reactant gases have not reacted in the firstregenerative bed.
 20. The process of claim 1 wherein the cyclicreverse-flow reactor system is an asymmetric reaction chemistry systemcoupling the exothermic reaction with an endothermic reaction.
 21. Theprocess of claim 19 wherein the endothermic reaction of the cyclicreverse-flow reactor system comprises steam reforming, carbon dioxidereforming, pyrolysis, catalytic cracking, dehydrogenation, dehydration,or combinations thereof.
 22. The process of claim 20 wherein thepyrolysis reaction comprises steam cracking reactions of ethane, naptha,gas oil or combinations thereof.
 23. The process of claim 20 wherein thedehydrogenation reaction comprises alkane dehydrogenation,alkyl-aromatic dehydrogenation, or combinations thereof.
 24. The processof claim 20 wherein the dehydration reaction comprises methanoldehydration, ethanol dehydration, or combinations thereof.
 25. Theprocess of claim 20 wherein the pyrolysis reaction includeshydropyrolysis reactions comprising methane hydropyrolysis to produceacetylene.
 26. The process of claim 20 wherein the pyrolysis reactioncomprises H₂S pyrolysis.
 27. The process of claim 1 wherein the firstreactant is a fuel comprising CO, H₂, hydrocarbon(s), oxygenates,petrochemical, or a mixture thereof.
 28. The process of claim 1 whereinthe second reactant is an oxygen containing gas.
 29. The process ofclaim 26 wherein the oxygen containing gas is air.
 30. The process ofclaims 26 or 27 wherein the first reactant, or the second reactant, orboth, further comprise non-combustible gas or gases.
 31. The process ofclaim 1 wherein the cyclic reverse flow reactor system is a symmetricreaction system.
 32. The process of claim 30 wherein the exothermicreaction comprises full oxidation or partial oxidation.